IE55396B1 - Container,particularly for milk products and machine and process for manufacturing such containers - Google Patents

Abstract

1. A container at least partially made of plastic, and in particular a container for milk products, the container including a tubular side wall and a bottom fixed to the side wall, the container being characterized in that the side wall (1) is constituted by a rectangular thermoplastic sheet (2) having its short sides welded together to constitute a closed contour, and by two end closure members substantially perpendicular to the side wall and respectively constituting the bottom (4) and the lid (3), each closure member (3, 4) including a groove (10) for receiving an edge of the side wall (1), and the edge being ultrasonically welded in the corresponding groove (10).

Description

2 5 ο 3 y 6 The present invention relates to a container made sc least partially of plastics material (hereinafter referred to as "plastic" for short) and intended particularly, hut not exclusively, for packaging fresh milk products such as yoghurt, and to a machine 5 and method for making containers of this type.

Pots made of plastic have to a very large extent replaced pots made of waxed card or of glass as yoghurt containers.

Compared with glass pots, plastic pots have the advantages of being lighter, less fragile, and more suitable for having 10 marking printed directly on the pot. Unfortunately, plastic containers (which are generally made of polystyrene or of polypropylene) do not provide some of the advantages that glass containers provide in use: in particular they do not provide such good isolation from the surrounding medium. Thus, 15 plastic, and in particular polystyrene, is relatively porous to gases normally present in the atmosphere, such as oxygen, carbon dioxide, and water vapor. These gases can diffuse through the wall of the container and spoil the quality of the product, even during its normal shelf life. As a result the 20 taste is rapidly degraded.

It is a first object of the present invention to provide a container which enables the quality of the product to be fully conserved during its shelf life.

Also, conservation of the product contained in the 25 container depends in part on the precautions taken when the container is filled. Another object of the invention is to provide a container which can be sterilized by purely physical means, which is in line with present trends in regulations.

Further, currently used containers are constituted by a 30 hollow body which is closed by a lid or cap that is sealed or clamped in place. Pots may thus be manufactured by blowing or by injection making use of the properties of plastics. This solution allows one to obtain the body of the container in one operation, followed by closure thereof, after filling, by a second operation. Unfortunately, since 35 the site of container manufacture is genferally distant from the site of product manufacture and 3 container filling, the empty containers need to be transported (eg. by road), which results in considerable empty space being transported in spite of various container-stacking techniques.

A further object of the invention is to provide a container which is formed immediately before being filled, thereby improving transport efficiency and facilitating perfectly sterile filling conditions.

Suzuki's US patent N° 4 187 768 describes the manufacture of a container made of paper which has one face covered in a thermoplastic film. The container is built up from a bottom component and a side wall component which are welded together ultrasonically. The periphery of the bottom component is folded in such a manner that the fold is surrounded by another fold in the bottom of the side wall. The top of the container is hemmed. The method described in the said patent is long given the need to perform the folding and the fact that it always takes longer to weld plastic to paper than it does to weld plastic to plastic. The weld is performed by relative displacement between the container and an ultrasonic probe which further increases the manufacturing time. An additional factor is that the bigger the container the longer it takes to manufacture using the method described in the said US patent.

Another object o£ the present invention also enables containers of any cross section to be manufactured at a rate which is substantially independent of the size of the containers.

Finally, for practical purposes, milk products are generally packed in individual or unit portions. Both for practical purposes and for commercial reasons, it is desirable for such unit portions to be grouped in twos, fours, eights or twelves, and it may also be desirable for the milk products in such groups to be varied, ie. with adjacent containers containing different products. Dividing the product up into unit portions and bringing together different products into a single group both add to the cost of packaging. Furthermore, for reasons of mechanical strength, such groups generally need additional overall packaging which is usually a carton.

Another object o£ the present invention is to provide a 4 container which is easily grouped with" other like containers without requiring a group formed in this manner to be packed in a carton, thereby considerably reducing overall costs.

The present invention provides a container at least partially made of plastic, and in particular a container for milk products, said container comprising a tubular side wall and a; bottom fixed to the side wall, said side wall being constituted by a rectangular thermoplastics sheet having its short sides welded together to constitute a closed contour, and by two closure members substantially perpendicular to the side wall and respectively constituting a lid and said bottom, each closure member including a groove for receiving an edge of the side wall and the edge being ultrasonically welded in the? corresponding groove.

The components are thus positioned relative to one another somewhat automatically'by the edges of the end walls being received in the grooves. Once properly placed, they are relatively easily welded in order to seal the joint. It may be noted that the assembled components for welding have the advantage of concentrating ultrasounds, and the resulting weld is of good quality.

The aforementioned closure members will be respectively designated as follows by bottom for the lower member welded before the filling of the pot and by cap or lid for the upper member welded after the filling of the pot.

The end closure members are preferably constituted by a bottom and a lid which are made by injection molding, while the sheet which is made up into the side wall is preferably extruded.

Thus the side wall or side, the lid and the bottom are flat while being transported to the filling site which permits optimum use to be made of the means of transport used.

The present invention also provides a machine for manufacturing such containers, said machine comprising at least one ultrasonic welding electrode; means for unstacking the rectangular sheets, the 5 bottom-forming closure members and the top forming closure members; means for sterilizing the unstacked components; means for folding the sheets and for ultrasonically welding the short sides thereof to 10 constitute side walls; means for assembling one edge of the side wall inside the groove or a bottom extending substantially perpendicularly thereto; a welding head for ultrasonically welding the edge 15 of the side wall in the groove or the bottom, said head being one of the welding electrodes; means for filling the container with a portion of the product; means for snap-fitting a lid to the top edge of 20 the side wall so that the top edge enters the groove in the lid substantially perpendicularly thereto; and a welding head for ultrasonically welding the lid onto the top edge of the side wall. 6 The invention also provides a method of manufacturing a container, in particular for milk products, the method comprising: forming rectangular thermoplastics sheets by 5 extrusion with one of the faces thereof being embossed; making closure members by injection to respectively constitute the lids and the bottoms with each member having a groove; 10 ultrasonically welding together the short sides of the rectanglular sheet to constitute a side wall having a closed contour; inserting the bottom edge of the wall into the groove of the bottom-forming closure member 15 extending substantially perpendicularly to the wall, and ultrasonically welding the edge inside the groove; and after filling the container, mounting the lid-forming closure member on the top edge of the 2o side wall in such a manner that the edge is inserted inside the groove of the lid substantially perpendicularly to the lid, and performing ultrasonic welding. 7 All the components are thus fed to the machine in flat or sheet form. This greatly facilitates sterilization of the components, eg. by means of ultraviolet radiation or the like, and the subsequent operations can readily be performed under an inert atmosphere.

Making the side walls by extruding sheet material has several advantages. Firstly, a plurality of layers or plies may be extruded simultaneously. The resulting composite sheet can be made impermeable to gas by including an impermeable layer, thereby improving storage of the product in the container. Secondly there is no difficulty in marking the external faces of the container by printing. Thirdly, there is no need for any waste material, which is of considerable importance when dealing with composite sheets, since it is difficult to recycle multilayer offcuts.

When fresh milk products are transported, the vibrations due to the transport have a pumping effect on the products such that serum separates from the mass of the yoghurt or other product. A prior technique for reducing this drawback consists in using generally conical containers with their larger diameter ends at the bottom. This shape prevents the yoghurt from moving upwards against the shrinking diameter of the container. Unfortunately such containers do not lend themselves to nesting when empty nor to stacking when full. Containers in accordance with the present invention are straight sided with the side walls extending perpendicularly to the end closure members. This ensures that the resulting structure is mechanically strong enough for several layers of full containers to be stacked on top of one another. In order to reduce the above-mentioned "pumping" effects, the interior faces of the straight sided walls are 8 advantageously embossed during extrusion of the side wall sheet so as to "key" the yoghurt to the wall and thus prevent it from moving relative to the container during transport.

An embodiment of the invention is described by way of 5 example with reference to the accompanying drawings, in which: Figure 1 is an exploded perspective view of a group of containers in accordance with the invention; Figures 2 and 3 are respectively a front view and a vertical section through a single container; 10 Figure 4 is a perspective view of a single extruded sheet for making up into the side walls of a container; Figure 5 is a cross section through multilayer wall material; Figure 6 is a diagrammatic perspective view of an extruder 15 for extruding side wall sheet; Figure 7 is a block diagram of a container forming machine; Figure 8 is a perspective diagram of the Figure 7 container forming machine; Figure 9 is a partially cut-away perspective view of a 20 machine for shaping the side wall; and Figure 10 is a partially cut-away perspective view of means for advancing containers through a filler machine.

Figure 1 is an exploded perspective view of a group of four containers, each of the type shown in a front view in 25 Figure 2 and in cross section in Figure 3- In accordance with the invention, each container comprises three portions, a side wall 1, a cover or lid 3» and a bottom 4· The bottom 4 and the lid 3 have grooves 10 which receive the bottom and the top edges respectively of the side wall 1 and which are ultra-30 sonically welded thereto. This method of welding is preferred over other known methods because of its speed and because it conserves the organoleptic characteristics of the container.

The side wall 1 is obtained by lap welding the ends of a plastic sheet 2 (see Figure 4) in which fold lines or creases 6a are preformed during extrusion. 9 As can be seen more clearly in Figure 3> the lid 3 has a bottom 12 which is lower than the top edge of the side wall 1. The bottom closure member 4 has a bottom 13 which projects beyond the bottom edge of the side wall 1. Thus the lid is concave and the bottom is convex in the embodiment shown. The opposite arrangement could be used with a convex lid and a concave bottom. The profiles of the lid 3 and the bottom 4 are complementary so that the convex bottom of one container can be received in the concave lid of a another container, thereby stacking the containers with their side walls 1 accurately aligned. This ensures maximum mechanical strength for such a stack, and normal stacking and handling loads are adequately supported. The lid 3 and the bottom 4 have rims defining the grooves 10 in such a manner that the top and bottom edges of the side wall 1 are securely received therein, and may be even snap fitted thereto, prior to the above-mentioned welding.

This ensures accurate assembly of the three parts.

In the drawings, the containers are shown as pots of square section. This is an advantageous configuration in that it enables compact groups of containers to be obtained, thereby not wasting space. However, other cross sections are possible, and in particular a circular section could be used.

Figure 4 is a perspective view of a sheet 4 prior to folding into the shape of the side wall 1. The sheet has an internal face 5 and an external face 7 (relative to the assembled container). The external face 7 is smooth and is intended to receive decoration and/or information concerning the product contained in the container. The internal face 5 is embossed with a checkered pattern of projecting ribs 6.

Although it is known to use ribs on the walls of containers, this has previously been for the purpose of strengthening the container walls, rather than for providing the container with means for gripping the product, ie. for keying the product to the wall. This gripping or keying function is enhanced by using a diagonal pattern as shown, but other patterns could alternatively be used. The advantage of allowing a "thick" product such as yoghurt to grip the walls is that it remains 10 homogenous inside the container in spite of the shocks associated with transporting the containers after they have been filled. The embossing does also contribute to overall strength of the container, but its resistance to vertical 5 crushing lies principally with its side wall being disposed vertically and with the welding to the end parts (the lid 3 and the bottom 4) giving the structure adequate rigidity.

The sheet 2 is made by extrusion, and if the side wall 1 is to be of polygonal cross section, crease marks 6a are 10 preformed in the sheet during extrusion to facilitate subsequent folding. The crease marks 6a are advantageously slightly curved in shape.

As mentioned above, it is necessary for unit portions to be grouped together into convenient sized units for 15 commercialization. An example of such a grouping is shown in Figure 1. Grouping is generally achieved by associating the top and/or bottom end members in groups of at least two. In the example shown, four lids 3 are associated. This association is obtained at the same time as the lids are 20 formed, eg. by hot pressing or by injection molding. Tear-off strips 8 are provided between adjacent associated lids. The strips 8 extend over a portion only of the facing sides of the lids, and in the arrangement of four lids shown in Figure 1, a central hole 9 is left empty. Such a hole enables a handling 25 tool (not shown) such as a barbed rod to be passed through several layers of stacked groups of containers, thereby ensuring that the layers are maintained relative to one another. The central hole can also be used when transporting a single group of containers by hand.

Naturally, on arrival at their final destination, the containers must be easy to open. A line of weakness 14 is thus provided in each lid 3 to delimit a cap 11 which can be removed from the lid. To facilitate its removal, the cap incorporates a pull tab (not shown).

Given the shape of the end members 3 and 4, and the strength of the side walls 1 against vertical crushing, several groups of containers may be superposed so as to constitute a 1 1 uniform assembly. This arrangement greatly improves the efficiency with which vehicles and storage areas can be filled, for example up to 2.2 times as much milk product may be stored in a given volume compared with prior art containers. Further, the containers no longer need to be packed into a carton, thereby considerably reducing cost. Once a predetermined quantity of containers have been brought together both horizontally and vertically, they may simply be strapped together to prevent them, coming apart. In the example described, vertical assembly and positioning is due to the convex bottoms being received in the concave lids. The opposite could just as well be true with convex lids being received in concave bottoms. The essential point is to ensure that vertical forces are directly transmitted from side wall to vertically adjacent side wall.

Figure 5 is a cross section through the sheet 2 or through a lid or a bottom. As mentioned above, preferred embodiments of the present invention improve conservation of the product stored in the container. This is achieved by improving the impermeability of the walls to gases. To do this, merely increasing the thickness of the walls rapidly encounters practical manufacturing limits. Gas impermeability is better obtained by making the walls of the container from a layered material including at least one layer which is impermeable to the gases that ought not to be allowed to diffuse into the container, eg. oxygen. The structure of such a layer constitutes a barrier to the diffusion of one or more gases through the wall. Suitable barrier materials include copolymers of ethylene-vinyl-alcohol (EVAI) and polyvinylidenes (PVDC). Figure 5 is a cross section through such a multilayer material including an external layer 7, an internal layer 5» and a middle layer 15· In some cases other materials are added to these main layers to ensure proper adhesion between the layers. The internal and external layers 5 and 7 may be constituted by polystyrene or polypropylene, with the middle layer 15 being made of EVAI or PVDC.

The barrier made in this manner conserves the taste "old fashioned" products throughout the shelf life without requiring anti-oxidizing chemical preservatives and while using modern materials that can be extruded rather than being blown.

Figure 6 shows the process for extruding the side walls 1. Three extruders 16, 17, and 18 deliver three streams of pasty material to a shaping die 19 which outputs three layers of material 5, 7 and 15· A set of rolls 20 provide the embossing 6 of the internal surface (ie. the surface inside the finished container). The three-layer sheet is then cooled at 21 and its external face 7 receives printing from an inking roll 25 and a printing roll 22. The printed face is then dried in an oven 24 and the sheet 2 is cut to size by a guillotine 25 which cuts off lengths of sheet 2 equal to the desired height of the containers. The width of the sheet coming from the die 19 is equal to the perimeter of the finished side wall plus the welding overlap. The lengths of sheet 2 are counted, stacked and packaged at 26. It may be observed that there is no wastage of material in the manufacture of the sheets 2, which is of particular importance for a multiple layer material.

The lids 3 and the bottoms 4 may be shaped from the same material as the side walls 1, or they may be made from some other material. They may be hot pressed or they may be injection molded. Depending on requirements they may be of different colors so that if a mixture of products is offered in the same group of containers, then each product may be identified by color coding one or both ends of the containers.

As mentioned above, the lids 3 are made in groups of two, four, eight or twelve and the containers are welded thereon without breaking the grouping. The bottoms 4 may likewise be made in groups, or else they may be individually applied. Alternatively the bottoms may be grouped for the purposes of grouping containers and the lids may be applied individually.

By way of typical example, the machines that fill the containers with individual portions operate at a rate of about 40,000 portions an hour. It is thus desirable for the machines which make the packaging to operate at a similar rate. Figures 7 1 3 and 8 are respectively a block diagram and an exploded perspective view of a machine for making containers in accordance with the invention and intended to occupy the same premises that are used for making the content. As mentioned above the components 5 for making the containers are made elsewhere and are delivered flat and in sheet form which makes the loading of trucks for transport highly efficient in comparison with the transport of fully formed empty containers. As shown in Figures 7 and 8, a machine includes three unstacking stations 27, 28 and 29 for 10 the sheets 2, the bottoms 4 and the lids 3 respectively. Each unstacking station is followed by a respective sterilizer 34, eg. using ultraviolet radiation, with the components being sterilized while still flat. The sheets 2 as unstacked at 27 are conveyed to a shaping stage 30 where they are folded in 15 four and welded along a generator line. In parallel with this operation, a set of bottoms 4 is delivered to a station 30 and is assembled to the tops of the tubular side walls 1 of a group of pots. Pressure is applied to ensure that the edges of the side walls 1 penetrate into the grooves 10. This assembly then 2o passes an ultrasonic welding head 31 thus completing the pots per se. The pots are then turned over and delivered to a filling station 32 which is followed by means for applying lids or groups of lids thereto and then means 35 for welding the lids 3 to the pots. A station 36 automatically places groups 25 of filled pots onto a pallet.

Figure 9 is a partially cut away perspective view of a station for making the side walls 1 from the sheets 2. The unstacking station 27 is of conventional type. After passing through the ultraviolet radiation at 34 the sides of the side 30 wall are folded by a combination of guides 39 and 41 and they are welded along the join line by an ultrasonic probe 40.

There is a small overlap where the sides are welded together.

Figure 10 is a partially cut away perspective view of the station 35 for filling the pots. After the pots have been 35 turned the right way up, they enter a housing 45* They are driven along the housing 45 by an endless belt 51 which is caused to advance stepwise by a roll 42 which is driven from a 14 drive shaft 44 via a Maltese cross type of cam 43· The purpose of such stepwise advance is to ensure that the pots are stationary during filling and during subsequent welding of the lid. The pots are simultaneously pushed by a piston 46 which is driven from a gear wheel 49 which co-operates with an eccentric arrangement 48 including a cam 50 which is connected to the piston 46 by a lever which is hinged about a fixed shaft 47* The assembly is designed so that the stroke of the piston 46 is substantially equal to the step size of the endless belt 51 as driven by the roll 42.

Given the structure of the containers, the container manufacturing machine is advantageously modular comprising the following main modules: side wall shaping; bottom placement; product filling; and lid placement.

Secondary modules may include, for example, automatic stack insertion modules; automatic quality control modules (shown diagraromatically at 52 in Figure 8) for obtaining statistics; and an automatic pallet loading module. The movements of the various operations for packaging the product do not require a continuously moving assembly line. The movements are of small amplitude and do not require high torque. The accuracy which can be obtained on the components means that the complex positioning means of conventional machinery can be avoided. In the machine described above, each pot constitutes its own positioning means. This considerably simplifies sterilization and and the maintenance of sterile conditions along the entire production line, thus saving on equipment costs. Costs are also kept down by the items used in the line, such as the ultrasonic welding probes and the pot filling machines, being standard commercially available items.

The present invention may be used for packaging products which are in powder, pasty, or liquid form, and which need not be food products. It provides the following novel combination of characteristics: good product conservation; no additional 15 packaging carton for groups of containers; excellent marking due to information and decoration being printed on surfaces while they are flat; ease of grouping containers and subsequently of breaking up the groups; the product is itself 5 keyed to the walls of the container.

Claims (14)

1. A container at least partially made of plastic, and in particular a container for milk products, said container comprising a tubular side wall and a bottom fixed to the side wall, said side wall being constituted by a rectangular thermoplastics sheet having its short sides welded together to constitute a closed contour, and by two closure members substantially perpendicular to the side wall and respectively constituting a lid and said bottom, each closure member including a groove for receiving an edge of the side wall and the edge being ultrasonically welded in the corresponding groove.

2. A container according to claim 1, wherein the internal face of the side wall is embossed and the external face of the side wall is smooth.

3. A container according to claim 1, wherein the external face of the side wall is decorated.

4. A container according to any preceding claim, wherein the external surface of the lid-forming closure member is complementary to the external surface of the bottom-forming closure member with the external surface of one of the closure members being concave and the external surface of the other closure member projecting from the edges of the side surface, the extent of the projection being substantially equal to the concave depth such that after the containers have been filled, closed and stacked, the edge of one side wall is aligned with the side wall of the adjacent container in the stack.

5. A container according to any preceding claim, wherein the lid includes a tear-off cover.

6. A container according to any preceding claim, wherein at least one of the components is constituted by a multiple layer complex constituting a barrier to gas diffusion.

7. A group of containers according to any preceding claim, wherein at least one of the closure members is connected to the corresponding closure member of an adjacent container by means of a tear-off strip.

8. A group of containers according to claim Ί, wherein at least two adjacent containers in the group include different markings and/or closure members of different colours.

9. A machine for manufacturing containers according to any preceding claim, said machine comprising: at least one ultrasonic welding electrode; means for unstacking the rectangular sheets, the bottom-forming closure members and the topforming closure members; means for sterilizing the unstaeked components; means for folding the sheets and for ultrasonically welding the short sides thereof to constitute side walls; 18 means for assembling one edge of the side wall inside the groove or a bottom extending substantially perpendicularly thereto; a welding head for ultrasonically welding the edge 5 of the side wall in the groove or the bottom, said head being one of the welding electrodes; means for filling the container with a portion of the product; means for snap-fitting a lid to the top edge of 10 the side wall so that the top edge enters the groove in the lid substantially perpendicularly thereto; and a welding head for ultrasonically welding the lid onto the top edge of the side wall. 15

10. A method of manufacturing a container, in particular for milk products, the method comprising; forming rectangular thermoplastics sheets by extrusion with one of the faces thereof being embossed; 20 making closure members by injection to respectively constitute the lids and the bottoms with each member having a groove; ultrasonically welding together the short sides of the rectanglular sheet to constitute a side wall 25 having a closed contour; inserting the bottom edge of the wall into the groove of the bottom-forming closure member extending substantially perpendicularly to the wall, and ultrasonically welding the edge inside the groove; and 30 after filling the container, mounting the lid-forming closure member on the top edge of the side wall in such a manner that the edge is inserted inside the groove of the lid substantially perpendicularly to the lid, and performing ultrasonic welding.

11. A container according to claim 1, substantially as hereinbefore described with particular reference to and as illustrated in Figs. 1-3 of the accompanying drawings.

12. A machine according to claim 9 for manufacturing containers as claimed in any one of claims 1-9 and 11, substantially as hereinbefore described with particular reference to and as illustrated in Figs. 6-10 of the accompanying drawings.

13. A method according to claim 10 of manufacturing a container, substantially as hereinbefore described with particular reference and as illustrated in Figs. 6-10 of the accompanying drawings.

14. A container whenever manufactured by a method claimed in claim 10 or 13. F. R. KELLY & CO., AGENTS FOR THE APPLICANTS.